Green’s Dictionary of Slang

(US) the buttocks.

1984		in L.A. Times 11 Oct. V 25: Layin’ on your gluts [sic] inhalin’ [i.e. beer] is not workin’ out [HDAS].
1992		M. Leyner Et Tu, Babe (1993) 63: Muscle mass, density, ripped definition, triceps, biceps, pecs, lats, glutes, intensity, stamina, endurance.
2000		F.X. Toole Rope Burns 74: In two weeks she [...] learned how to use her thighs, glutes, and leg biceps the way fighters use them.
2007		C. Goffard Snitch Jacket 165: What you need is some ab work [...] some military presses, quads, lats, and glutes.